This invention relates to pyrazolone magenta dye-forming couplers having a particular aryl thio coupling-off group that enables improved photographic properties, improved manufacturing and handling characteristics and to photographic materials and processes employing such couplers.
There are numerous properties and characteristics that must be controlled in the successful design of a photographic element. Among these are light stability, dark stability, developer retention, dye density, leuco-dye formation, printability, minimization of continued coupling and coupling efficiency. Light stability refers to the ability of the element, e.g. a color print, to withstand light exposure without degradation. Dark stability refers to the ability of the elements to withstand dark storage, e.g. in a photo album. Developer retention refers to the ability of the conventional processing bath to effectively remove any remaining unreacted developer from within the film structure so that such developer will not over a period of time continue to react with the coupler and form additional undesired dye density. Sufficient dye density is essential to obtaining the desired degree of color contrast and intensity. Leuco-dye is an intermediate stage of dye formation all of which must have been converted to dye by the end of the development process (e.g. 90 seconds for negative-positive or 3 minutes 15 seconds for color negative) otherwise the dye density and corresponding color balance will be unstable. When a coupler tends to form a stable leuco-dye, a layer of finely divided silver halide ("Lippman Silver") is often employed to oxidize the leuco-dye to its final form. Printability refers to the compatibility of the light absorbance curve as a function of wavelength as compared to the curve employed as a printing standard in high speed printing. Continued coupling refers to the extent to which the coupler will undesirably react with oxidized developer formed in the bleach bath resulting in stain, and coupling efficiency refers to the quantity of a coupler necessary to achieve a given dye density.
Due to the complexity of the organic couplers employed in modern photography, it has become exceedingly difficult to discover materials which satisfy these diverse needs. So-called four equivalent 3-anilino pyrazolone couplers have provided magenta dye images having useful properties. Examples of such compounds are described in, for example, U.S. Pat. Nos. 3,907,571, 3,928,044, 3,935,015, 4,199,361 and 3,519,429. An example of one such pyrazolone coupler, described in, for example, U.S. Pat. No. 3,519,429 is herein designated as comparison coupler C-1 and is represented by the formula: ##STR2## This prior art coupler has a number of disadvantages. Since C-1 is a four-equivalent coupler, more silver halide and coupler must be used to obtain adequate dye yield when compared to two-equivalent couplers. This increases the costs associated with this type of coupler. Also, the dye light stability is less than desired and the dye dark stability is quite poor. Further, the coupler itself causes substantial yellow stain in areas of minimum density, especially when kept under humid conditions.
Examples of so-called 2-equivalent 3-anilino 4-(arylthio) pyrazolones are described in, for example, U.S. Pat. No. 4,413,054, Japanese published patent application 60/057839, U.S. Pat. Nos. 4,351,897, 4,900,657, and 4,876,182. An example of such a pyrazolone coupler described in, for example, U.S. Pat. No. 4,413,054 is designated herein as comparison coupler C-2 and is represented by the formula: ##STR3## The presence of an alkoxy group in the ortho position on the phenylthio coupling-off group of coupler C-2 has provided advantageous properties. However, this type coupler has not been entirely satisfactory due to formation of undesired stain in a color photographic silver halide element upon exposure and processing and does not provide desired printability characteristics for rapid machine processing. The coupler C-2 does not achieve full dye density, especially when the exposed color photographic element is machine processed without the presence of Lippman fine grain silver halide being present in the photographic element. It has been desirable to reduce or avoid the need for added Lippman fine grain silver halide without diminishing dye density in the processed color photographic silver halide element. The prior art coupler C-2 does not answer this problem.
Another example of a pyrazolone coupler known to the art is described in U.S. Pat. No. 4,853,319 is designated herein as comparison coupler C-3 and is represented by the formula: ##STR4## The presence of an acylamine group in the ortho position on the phenylthio coupling-off group of coupler C-3 has provided advantageous properties. This coupler does not require Lippman fine grain silver halide in order to obtain adequate dye density upon rapid machine processing. However, this type of coupler does suffer from unwanted gains in both green and blue density in unexposed areas upon standing in the dark. Another problem with couplers of this type is their propensity to retain developer after processing, which can lead to an increase in unwanted density or stain upon standing. Further, although the dye light stability for this class of couplers is good, additional improvement in dye light stability is still needed.
Another example of a pyrazolone coupler known to the art is described in U.S. Pat. No. 4,853,319 is designated herein as comparison coupler C-4 and is represented by the formula: ##STR5## The synthesis of this type of coupler is problematic. The ballast portion of the coupling off group is made through the reaction of the ballasted phenol, sodium hydroxide, acetone and chloroform and involves a highly reactive carbene intermediate. The explosion hazard associated with this material is unacceptable from a safety standpoint. Therefore, this route is not amenable to synthesis on a production scale. Also, only symmetrical dimethyl-substituted acylamine ballasted coupling off groups can be obtained. Reactants other than acetone do not work satisfactorily in this reaction. An additional limitation is that the coupling reaction works best for phenols with either no ortho substituent or, at most, a small ortho substituent. This further limits the scope of the reaction. In a photographic element, the light stability of this type of coupler is not as good as is desired, and the dye from this coupler has high unwanted blue absorbance and therefore inaccurate color reproduction. The symmetry of the molecule leads to dye aggregation and solubility problems.
Another example of a pyrazolone coupler known to the art is described in Japanese published application 60-057839 is designated herein as comparison coupler C-5 and is represented by the formula: ##STR6## This type of coupler does not produce sufficient dye density, especially in a rapid access format, to be useful as a coupler in a photographic element. In addition this coupler exhibits poor hue and unwanted absorbance characteristic of the 3-acylamino type pyrazolone couplers.
Other examples of pyrazolone couplers known to the art are described in U.S. Pat. Nos. 4,853,319 and 4,929,540 are designated herein as comparison C-6 and C-7 and are represented by the formulas: ##STR7##
These couplers and comparison couplers C-2, C-3 and C-4 all form dyes which undesirably aggregate which is of primary concern in color negative processing. The result of this aggregation is an unsymmetrical bulging of the dye hue curve on the hypsochromic side (shorter wavelength). In negative-positive systems, it is important for good color reproduction to minimize the unwanted blue density in the green layer, expecially at 440 nm and 480 nm (where printers and color paper measure blue density, respectively), and to maximize green density at 550 nm (where printers and color paper measure green density). Comparison couplers C-2, C-3, C-4, C-6 and C-7 all show an undesirable increase of blue density because of aggregation, and this leads to poor color reproduction of the color print. The coupler of the invention, on the other hand, does not exhibit this undesired blue density to such an extent and is far more satisfactory from the printability standpoint.
One further example of a pyrazolone coupler is shown in U.S. Pat. No. 4,876,182 and has the formula: ##STR8## This compound has provided good results but has exhibited a less than desired coupler efficiency.
It has been desired to provide a new pyrazolone coupler having a coupling-off group in a color photographic silver halide element and process which is capable of forming a magenta dye image of good stability, with high dye yield and low unwanted blue absorption as well as high activity and reduced incidence of continued coupling. Additionally, it is desired to provide such a coupler which displays excellent thermal stability in areas of no light exposure and which has no tendency to retain color developer after photographic processing. Further, it has been desired to provide a new pyrazolone coupler which provides all of the above attributes and can be produced in good yield by a convenient safe procedure that is amenable to large scale production.